Actuator support structure and pump device

ABSTRACT

A piezoelectric pump includes a leaf spring including a disc portion defining an actuator, an outer frame portion defining a housing, and an elastic support portion. The actuator flexurally vibrates from a center portion of a principal surface thereof to an outer periphery thereof. The elastic support portion includes a beam portion and connection portions and elastically supports the disc portion on the outer frame portion. The beam portion extends in a gap between the disc portion and the outer frame portion in a direction along an outer periphery of the disc portion. A first of the connection portions connects the beam portion to the disc portion. Second and third connection portions are offset from the first connection portion and connect the beam portion to the outer frame portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an actuator support structure thatsupports an actuator which flexurally vibrates and a pump device thatincludes the actuator support structure and conveys fluid.

2. Description of the Related Art

A thin pump device has been developed which is used for conveying airfor a fuel cell system and other devices, and controls the flow of fluidby using an actuator that flexurally vibrates (e.g., see InternationalPublication No. 2008/069264).

FIG. 1 is a diagram illustrating an example of an existing pump deviceand its action.

The pump device 100 includes an actuator 110 including a vibration plate111 and a piezoelectric element 112 and an opposed plate 101 disposed soas to be adjacent to and opposed to the vibration plate 111. Thevibration plate 111 is made of metal and fixed at the entire outerperipheral portion thereof to the opposed plate 101. The piezoelectricelement 112 is attached to a center portion of the vibration plate 111.The opposed plate 101 includes a first opening 102 disposed at aposition that faces the center of the actuator 110 and a second opening103 disposed at a position that faces the actuator 110 so as to bepositioned outward of the piezoelectric element 112. In this pumpdevice, when a voltage of a predetermined frequency is applied to thepiezoelectric element 112, the vibration plate 111 resonates in athird-order resonance mode, and in the vibration plate 111, a portionthat faces the first opening 102 and a portion that faces the secondopening 103 bend in opposite directions. By repeating this bending, thepump device 100 sucks fluid through one of the first opening 102 and thesecond opening 103 and discharges the fluid through the other of thefirst opening 102 and the second opening 103.

There is demand for the size of an electronic apparatus in which a pumpdevice is included to be reduced in size, and for the size of the pumpdevice to be reduced without reducing the pumping power (fluid pressureand flow rate). In addition, for the electronic apparatus, a decrease ina power-supply voltage is also demanded, and for the pump device, adecrease in a drive voltage is also demanded. However, the pumping powerof the pump device tends to decrease as the size is reduced or the drivevoltage is decreased. Thus, there are limits to the size reduction andthe drive voltage decrease.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a small-sized andlow-height pump device having high pumping power and an actuator supportconfiguration that is suitable for such a pump device.

An actuator support structure according to a preferred embodiment of thepresent invention includes an actuator, a side wall, and an elasticsupport portion. In addition, a pump device according to a preferredembodiment of the present invention includes an actuator, a housing, andan elastic support portion, and the housing includes a side wall and anopposed wall. The actuator preferably has a plate shape and flexurallyvibrates from a center portion of a principal surface thereof to anouter peripheral portion thereof. The side wall surrounds an outerperiphery of the actuator. The opposed wall is located so as to beadjacent to and opposed to the principal surface of the actuator and isprovided with a flow path hole in a center portion of a region facingthe actuator or in the vicinity of the center. A fluid flows in throughthe flow path hole.

The elastic support portion includes a beam portion, an actuatorconnection portion, and a side wall connection portion and connects andelastically supports the actuator to the side wall. The beam portionextends in a gap between the actuator and the side wall in a directionalong the outer periphery of the actuator. The actuator connectionportion connects the beam portion to the actuator. The side wallconnection portion is provided in a position that is offset from theactuator connection portion in the direction along the outer peripheryof the actuator and connects the beam portion to the side wall.

According to this configuration, the outer peripheral portion of theactuator is connected and elastically supported on the side wall, suchas the housing, via the elastic support portion. Thus, the outerperipheral portion of the actuator is not fixed as in the structureshown in FIG. 1, and the outer peripheral portion of the actuator can bedisplaced. In addition, the beam portion of the elastic support portionextends in the direction along the outer periphery of the actuator andthe actuator connection portion and the side wall connection portion arearranged so as to be offset from each other. Thus, the beam portion canbe configured in a substantially straight shape or in a substantiallycircular arc shape, and a sufficient beam portion length can be ensuredwithout folding the beam portion. Therefore, a wide range of beamportion lengths can be used without substantially reducing the size (inarea) of the vibration plate.

In the above-described configuration of the pump device, preferably, thebeam portion is configured to be connected to the actuator via theactuator connection portion at a position adjacent to a loop, or ananti-node of natural vibrations when the side wall connection portion isa fixing portion, and a natural vibration frequency of the naturalvibrations corresponds to a natural vibration frequency of the actuator.

In the above-described configuration, preferably, two of the side wallconnection portions are connected to both ends of the beam portion, andthe actuator connection portion is connected to a center portion of thebeam portion between both ends thereof.

In the above-described configuration, preferably, vibrations of the beamportion accompanying the flexural vibrations of the actuator arevibrations in a first-order resonance mode.

In the above-described configuration of the pump device, preferably, theactuator has a disc shape, for example.

In the above-described configuration of the pump device, preferably, theopposed wall includes a thin portion which is provided on an outerperiphery of the flow path hole and capable of flexurally vibrating, anda thick portion which is provided on an outer periphery of the thinportion.

According to various preferred embodiments of the present invention, theouter peripheral portion of the actuator is enabled to be displaced withflexural vibrations, the flexural vibrations of the actuator areprevented from being damped by constraint from the side wall portion,and the amplitude of the flexural vibrations is increased. Since theamplitude of the flexural vibrations of the actuator is increased,desired fluid pressure and flow rate are efficiently obtained in thepump device even when a drive voltage is low.

In addition, a wide range of the beam portion length can be set withoutsubstantially reducing the size (in area) of the vibration plate. Thus,various characteristic values, such as the elastic modulus and theresonant frequency of the beam portion, can be arbitrarily set. Thelarger the area of the vibration plate is, the higher the flow rate canbe ensured in the pump device. Moreover, when various characteristicvalues, such as the elastic modulus and the resonant frequency of thebeam portion, can be arbitrarily set, the amplitude of the flexuralvibrations of the actuator can be increased by appropriately settingvarious characteristic values.

Furthermore, if a moment load applied to the elastic support portionduring driving is excessively high, the elastic support portion maybreak. For example, if the beam portion has a configuration that isfolded back in a middle portion (e.g., a meandering shape), a momentload is applied to the folded-back portion so as to open the beamportion in opposite directions, and the beam portion is likely to breakat that position. For such a problem, in the above-describedconfiguration, the actuator connection portion and the side wallconnection portion are configured to be offset from each other. Thus,the beam portion can be configured in a substantially straight shape orin a substantially circular arc shape, the position to which the momentload is primarily applied is limited to the actuator connection portionor the side wall connection portion, and breakage of the beam portion isprevented. By setting the length of connection with the actuator or theside wall to be relatively long, the actuator connection portion and theside wall connection portion can be configured so as to be difficult tobreak.

The present inventors have discovered that when a state is provided inwhich the beam portion vibrates in an odd number-order resonance modewith flexural vibrations of the actuator, damping of the flexuralvibrations is effectively prevented. Therefore, when the elastic modulusand the resonant frequency of the beam portion are appropriately set andthe beam portion is vibrated in an odd number-order resonance mode, thebeam portion is configured to be connected to the actuator at a positionadjacent to the loop of the resonance of the beam portion. In thisstate, damping of the flexural vibrations is effectively prevented, andthe amplitude of the flexural vibrations is further increased.

Since the beam portion is preferably supported in a double-supportedstructure, the actuator connection portion provided in the centerportion of the beam portion does not deform in a twisting manner, andbreakage of the actuator connection portion is prevented.

When the vibrations of the beam portion are in the first-order resonancemode, the vibration amplitude of the beam portion is maximized anddamping of the flexural vibrations of the actuator is effectivelyprevented.

When the actuator has a disc shape, rotationally symmetrical (coaxial)flexural vibrations occur, and thus, an unnecessary gap does not occurbetween the actuator and the opposed wall in the pump device and theoperating efficiency is increased.

Since the thin portion capable of flexurally vibrating is preferablyprovided in the opposed wall, the thin portion also vibrates with thevibrations of the actuator. Thus, the substantive vibration amplitude isincreased and the fluid pressure and flow rate are increased in the pumpdevice.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a known pumpdevice and its action.

FIG. 2 is a schematic diagram of a piezoelectric pump according to afirst preferred embodiment of the present invention.

FIG. 3A is a schematic diagram illustrating the principle of action ofthe piezoelectric pump shown in FIG. 2.

FIG. 3B is a schematic diagram illustrating the principle of action ofthe piezoelectric pump shown in FIG. 2.

FIG. 4 is a perspective view of the piezoelectric pump shown in FIG. 2.

FIG. 5 is an exploded perspective view of the piezoelectric pump shownin FIG. 2.

FIG. 6 is a plan view of a leaf spring shown in FIG. 5.

FIG. 7 is a schematic cross-sectional view illustrating deformation ofthe leaf spring shown in FIG. 5.

FIG. 8 is a diagram showing fluid pressure-flow rate characteristics ofthe piezoelectric pump.

FIG. 9 is a plan view according to another example of a configuration ofthe leaf spring shown in FIG. 5.

FIG. 10 is an exploded perspective view of a piezoelectric pumpaccording to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, piezoelectric pumps that include piezoelectric elementswill be described as examples of a pump device that includes an actuatorsupport structure according to preferred embodiments of the presentinvention.

First Preferred Embodiment

First, a schematic configuration of a piezoelectric pump 1 according toa first preferred embodiment of the present invention and its basicpumping action will be described.

FIG. 2 is a schematic cross-sectional view of the piezoelectric pump 1according to the first preferred embodiment of the present inventionduring non-driving.

The piezoelectric pump 1 includes a housing 2, an actuator 3, and anelastic support portion 4.

The actuator 3 includes a piezoelectric element 3B attached to avibration plate 3A. In the piezoelectric element 3B, electrode filmswhich are not shown are preferably provided on substantially the entireupper and lower principal surfaces, respectively. The piezoelectricelement 3B is configured to extensionally vibrate when, for example, asquare-wave or sine-wave drive voltage of about 20 kHz is appliedbetween these electrodes. Because of the configuration of the actuator 3in which the piezoelectric element 3B is attached to the vibration plate3A that is a rigid body, rotationally symmetrical (coaxial) flexuralvibrations having a vibration direction that corresponds orsubstantially corresponds to a direction perpendicular or substantiallyperpendicular to a principal surface direction occur from a centerportion of the principal surface to the outer periphery in the actuator3.

The housing 2 includes, as a flow path, an inner space 5 accommodatingthe actuator 3 and the elastic support portion 4 and flow path holes 6Aand 6B communicating with the inner space 5. The inner space 5 isconfigured to include a cylindrical side wall 5A, a lower opposed wall5B provided so as to close a lower opening of the side wall 5A, and anupper opposed wall 5C provided so as to close an upper opening of theside wall 5A. The flow path hole 6A is provided in the vicinity of thecenter of a region of the lower opposed wall 5B which faces the lowerprincipal surface of the actuator 3. Preferably, the flow path hole 6Bis provided at a position outward of a region of the upper opposed wall5C which faces the upper principal surface of the actuator 3 in thepresent preferred embodiment.

The elastic support portion 4 connects the outer periphery of theactuator 3 to the side wall 5A and elastically supports the actuator 3such that the lower principal surface of the actuator 3 is arranged soas to face the lower opposed wall 5B with a small space therebetween orin a contact state during non-driving.

The piezoelectric pump 1 of the present preferred embodiment utilizesthe schematic configuration as described above.

FIGS. 3A and 3B are schematic diagrams illustrating the basic pumpingaction of the piezoelectric pump 1. The actuator 3 moves away from thelower opposed wall 5B by being driven and each of a near-center regionand a near-outer periphery region of the actuator 3 vertically vibrateswith a vibration amplitude of about several micrometers to several tenmicrometers, for example.

When the actuator 3 bends so as to be upwardly convex as shown in FIG.3A, the gap between the actuator 3 and the lower opposed wall 5Bincreases in the vicinity of the center of the actuator 3. Thus, thefluid pressure is low in the vicinity of the center of the gap and,thus, the fluid tends to flow in through the flow path hole 6A and thevicinity of the outer periphery of the gap. However, the gap in thevicinity of the outer periphery of the gap is relatively small and theflow path resistance is high, and thus, inflow of the fluid through theflow path hole 6A is dominant.

When the actuator 3 bends so as to be downwardly convex as shown in FIG.3B, the gap between the actuator 3 and the lower opposed wall 5Bdecreases in the vicinity of the center of the actuator 3. Thus, thefluid pressure becomes high in the vicinity of the center of the gapand, thus, the fluid tends to flow out through the flow path hole 6A andthe vicinity of the outer periphery of the gap. However, the space inthe vicinity of the outer periphery of the gap is relatively wide andthe flow path resistance is low, and thus, outflow of the fluid throughthe vicinity of the outer periphery of the gap is dominant.

The action described above is repeated with the resonant frequency of afirst-order mode of the actuator 3, for example, with a frequency ofabout 20 kHz. By so doing, the fluid pressure in the gap in the vicinityof the center of or in the vicinity of the outer periphery of theactuator 3 continuously varies with the flexural vibrations of theactuator 3, but on a time average basis, negative pressure always occursin the vicinity of the center and positive pressure always occurs so asto counterbalance to the negative pressure. Because of this, thepiezoelectric pump 1 sucks the fluid through the flow path hole 6A anddischarges the fluid through the flow path hole 6B. It should be notedthat in the piezoelectric pump 1, the flow path hole 6A may preferablybe opened to the air to perform positive pressure action, or the flowpath hole 6B may preferably be opened to the air to perform negativepressure action.

In addition, with this configuration, the average size of the gapbetween the actuator 3 and the lower opposed wall 5B varies depending onvariation of the pump load. In other words, in a state in which the pumpload is high, the pressure in the space located on a side of theactuator 3 opposite to the lower opposed wall 5B becomes high, and thus,the average size of the gap between the actuator 3 and the lower opposedwall 5B is reduced such that the spring force of the elastic supportportion 4 is balanced out. On the other hand, in a state in which thepump load is low, the pressure in the space located on the side of theactuator 3 opposite to the lower opposed wall 5B becomes low, and thus,the average size of the gap between the actuator 3 and the lower opposedwall 5B is increased such that the spring force of the elastic supportportion 4 is balanced out. Therefore, the size of the gap isautonomously adjusted in response to variation of the pump load.

Next, a specific example of a configuration of the piezoelectric pump 1will be described. FIG. 4 is a perspective view of the piezoelectricpump 1. The piezoelectric pump 1 includes a plurality of plate-shapedmembers that are laminated to one another, a flow path hole 6B todischarge fluid in an upper surface thereof, and a very small heightpreferably having an overall thickness dimension of, for example, about1 mm.

FIG. 5 is an exploded perspective view of the piezoelectric pump 1. Thepiezoelectric pump 1 includes a housing top plate 11, a spacer 12, apower-supply plate 13, an insulating spacer 14, the piezoelectricelement 3B, a leaf spring 15, a reinforcing plate 16, a spacer 17, athin metal plate 18, and a frame plate 19 arranged in this order fromthe upper surface side.

In this example, a portion of the leaf spring 15 defines the vibrationplate 3A, the piezoelectric element 3B is connected to the upper surfaceof portion, and the reinforcing plate 16 is connected to the lowersurface of the portion, to define the actuator 3. The reinforcing plate16 is provided to enhance the rigidity and adjust the resonant frequencyof the actuator 3.

It should be noted that in the actuator 3 having the configurationdescribed above, the members may preferably be connected to each otherusing a thermosetting adhesive, for example, and in such a case, warpagemay occur in the actuator 3 due to the differences in coefficient oflinear expansion between the members. In order to prevent such warpage,the coefficient of linear expansion of each of the leaf spring 15, thepiezoelectric element 3B, and the reinforcing plate 16 is preferablyselected such that thermal stress at the upper surface of the leafspring 15 and thermal stress at the lower surface of the leaf spring 15are balanced or substantially equal to one another. In addition, ifcompressive stress is designed to be applied to the piezoelectricelement 3B after the joining, the shock resistance of the piezoelectricelement 3B can be improved so as to make the piezoelectric element 3Bdifficult to break. For this purpose, a material having a sufficientlyhigher coefficient of linear expansion than coefficients of linearexpansion of the piezoelectric element 3B and the reinforcing plate 16is preferably used for the leaf spring 15. For example, phosphor bronze,German silver, or nickel silver, or other suitable material, having ahigh coefficient of linear expansion, is preferably used for the leafspring 15, and SUS430, which has a relatively low coefficient of linearexpansion, is preferably used for the reinforcing plate 16.

FIG. 6 is a plan view of the leaf spring 15. The leaf spring 15 ispreferably a rectangular or substantially rectangular plate made ofmetal and includes three elastic support portions 4, an outer frameportion 23, a disc portion 24, and an external connection terminal 29,for example. It should be noted that the external connection terminal 29projects outwardly from a corner in an outer periphery and is connectedto a drive circuit, and a drive voltage to drive the piezoelectricelement 3B is applied thereto.

The outer frame portion 23 preferably includes a circular orsubstantially circular opening surrounding the circumference of the discportion 24 and defines a portion of the housing 2. The disc portion 24preferably has a circular or substantially circular shape and definesthe actuator 3 together with the reinforcing plate 16 and thepiezoelectric element 3B as described above. It should be noted that theactuator 3 is preferably designed to have a natural vibration frequencyof about 20 kHz, for example, and is driven to resonate and flexurallyvibrates when a drive voltage of the same or substantially the samefrequency as this frequency is applied to the piezoelectric element 3B.The three elastic support portions 4 are provided in a gap (slit)between the outer frame portion 23 and the disc portion 24 preferably atintervals of about 120°, for example.

Each elastic support portion 4 includes a beam portion 25 and connectionportions 26, 27, and 28. The beam portion 25 extends in the gap betweenthe outer frame portion 23 and the disc portion 24 along the outercircumference of the disc portion 24, is connected at both ends thereofto the outer frame portion 23 via the connection portions 27 and 28, andis connected at a center portion thereof to the disc portion 24 via theconnection portion 26. The beam portion 25 includes a double-supportedstructure provided by the connection portions 27 and 28. With theelastic support portions 4 having such configurations, the disc portion24 and the actuator 3 are elastically supported by the outer frameportion 23 and the housing 2.

When the disc portion 24 is connected to the outer frame portion 23 viathe elastic support portions 4 as described above, a state in which theouter circumference of the disc portion 24 is not substantiallyrestrained, namely, a state in which the actuator 3 is not substantiallyrestrained by the housing 2, is provided. This allows the actuator 3 toflexurally vibrate such that the interval between the space of the outerperiphery of the actuator 3 and the lower opposed wall 5B changes asshown in FIGS. 3A and 3B. Accordingly, during driving, by the fluidpressure, the actuator 3 moves upward away from the lower opposed wall5B and freely vibrates in a non-contact state with respect to the loweropposed wall 5B. A desired vibration amplitude of the actuator 3 isensured, and high pressure and a high flow rate are obtained even with asmall-size and low-height structure. In addition, even when thefrequency of the flexural vibrations of the actuator 3 is increased suchthat the actuator 3 is driven in a non-audible range of about 20 kHz orhigher, a sufficient vibration amplitude is obtained and a desired flowrate and fluid pressure are ensured.

In addition, as shown in FIG. 6, each elastic support portion 4 ispreferably configured to include the beam portion 25 extending in theslit between the outer frame portion 23 and the disc portion 24 alongthe outer circumference of the disc portion 24, and the beam portion 25may be configured to have a wide range of lengths without substantiallyreducing the size (in area) of the disc portion 24. Therefore, eachelastic support portion 4 has high flexibility in setting its resonantfrequency (natural vibration frequency), and thus, enables the resonantfrequency to be set so as to substantially correspond to the frequencyof the flexural vibrations of the actuator 3, although it depends on thematerial and thickness of each member. Here, the dimensions of eachelastic support portion 4 are preferably selected such that the resonantfrequency (natural vibration frequency) thereof when the beam portion 25and the connection portions 27 and 28 are removed is substantially equalto the resonant frequency (natural vibration frequency) of the actuator3.

FIG. 7 is a schematic cross-sectional view illustrating a deformed stateof the beam portion 25. When the resonant frequency of each elasticsupport portion 4 corresponds or substantially corresponds to theresonant frequency (the frequency of the flexural vibrations) of theactuator 3, vibrations in the first-order resonance mode in which theconnection portion 26 to the actuator is the loop of the vibrationsoccur in the beam portion 25 with flexural vibrations of the actuator 3.In this case, the flexural vibrations of the actuator 3 are not dampedby the beam portion 25, and the amplitude of the flexural vibrations ofthe actuator 3 is maximized.

In addition, in the beam portion 25, a moment load is applied to theconnection portions 26, 27, and 28, which are connected to othermembers, in the directions indicated by arrows in the drawing. Thelengths of the respective connection portions 26, 27, and 28 in adirection connecting the actuator 3 and the side wall are selected suchthat breakage is not caused by the moment load. It should be noted thatthe beam portion 25 preferably has an arc shape in a top view and is notfolded back in a middle portion thereof. In a folded-back shape (i.e., ameandering shape, for example), a moment load is applied to afolded-back portion so as to open the folded-back portion in oppositevertical directions, and thus the elastic support portion has a highrisk of breakage. However, the piezoelectric pump 1, in which none ofthe beam portions 25 include a folded-back portion as in the presentpreferred embodiment, has a configuration in which the elastic supportportion is difficult to break and breakdown is unlikely to occur.

Even when the vibration mode of the beam portion 25 is an oddnumber-order resonance mode other than the first-order resonance mode,such as the third-order resonance mode, damping of the flexuralvibrations of the actuator 3 by the beam portion 25 is effectivelyprevented or minimized. However, in a high-order resonance mode, thevibration amplitude of the beam portion 25 is reduced, and thus,vibrations in the first-order resonance mode are preferable.

In the present preferred embodiment, the elastic support portions 4 arepreferably provided at three positions. However, the elastic supportportions 4 need only be provided in at least two positions, and theelastic support portions 4 may be provided in more than three positions,for example.

The leaf spring 15 having such a configuration enables the amplitude ofthe flexural vibrations of the actuator 3 to be increased such thatdesired fluid pressure and flow rate can be efficiently obtained in thepiezoelectric pump 1 even when the drive voltage is relatively low.

Referring back to FIG. 5, the configuration of each of the other memberswill be described.

The housing top plate 11, the spacer 12, the power-supply plate 13, andthe insulating spacer 14 define a housing on the upper surface side ofthe actuator 3, and openings 12A, 13A, and 14A provided in these membersdefine an inner space on the upper surface side of the actuator 3.

The housing top plate 11 is preferably a rectangular or substantiallyrectangular plate in which the flow path hole 6B is provided. Thehousing top plate 11 is preferably made of metal or resin, for example.The flow path hole 6B is a discharge hole that releases positivepressure within the housing and may be provided in any position in thehousing top plate 11 but is preferably provided in a position spacedaway from the center of the housing top plate 11 in the presentpreferred embodiment.

The spacer 12 is preferably a rectangular or substantially rectangularplate made of resin, for example, in which the opening 12A is provided,and is provided between the housing top plate 11 and the power-supplyplate 13. The power-supply plate 13 preferably is a rectangular orsubstantially rectangular plate made of metal, for example, in which theopening 13A is provided, and includes a power-supply terminal 13Bprojecting inwardly in the opening 13A and an external connectionterminal 13C projecting outwardly from a corner in the outer periphery.The power-supply terminal 13B is connected to an upper-surface electrodeof the piezoelectric element 3B via soldering or other suitable method,and the external connection terminal 13C is connected to a drivecircuit. The insulating spacer 14 is preferably a rectangular orsubstantially rectangular plate made of resin, for example, in which theopening 14A is provided, and functions to insulate the power-supplyplate 13 and the leaf spring 15 from each other.

The thickness of the insulating spacer 14 is preferably slightly largerthan the thickness of the piezoelectric element 3B, and the solderedposition of the power-supply terminal 13B is arranged at a positioncorresponding to the node of the flexural vibrations of the actuator 3.Thus, the power-supply terminal 13B does not substantially vibrate withthe flexural vibrations of the actuator 3. Accordingly, damping of theflexural vibrations of the actuator 3 by the power-supply terminal 13Bis prevented. In addition, the thickness of the spacer 12 is preferablyset to a thickness such that even when the actuator 3 flexurallyvibrates, the power-supply terminal 13B does not come into contact withthe housing top plate 11 and a sufficient interval is maintainedtherebetween. If the housing top plate 11 gets very close to theactuator 3, there is risk that the vibration amplitude of the actuator 3will be decreased due to the flow path resistance. Thus, by maintainingthe sufficient interval, a decrease in the vibration amplitude of theactuator 3 is prevented. With this configuration, the thickness of thespacer 12 is preferably substantially the same as that of thepiezoelectric element 3B.

In addition, the spacer 17, the thin metal plate 18, and the frame plate19 define a housing on the lower surface side of the actuator 3, and anopening 17A provided in the spacer 17 defines an inner space on thelower surface side of the actuator 3.

The spacer 17 is preferably a rectangular or substantially rectangularplate in which the opening 17A is provided, and is configured to ensurea space to accommodate the reinforcing plate 16. The thin metal plate 18is preferably a rectangular or substantially rectangular plate made ofmetal, for example, in which the flow path hole 6A is provided, anddefines the lower opposed wall 5B described with reference to FIG. 2.The frame plate 19 is preferably a rectangular or substantiallyrectangular plate made of metal, for example, in which an opening 19A isprovided, and is configured to include a thin portion and a thickportion in the lower opposed wall 5B.

Here, the thickness of the spacer 17 is preferably slightly larger thanthe thickness of the reinforcing plate 16 (by, for example, about 20μm), and thus, the lower surface of the actuator 3 (the lower surface ofthe reinforcing plate 16) faces the upper surface of the thin metalplate 18 (the lower opposed wall 5B) with a small gap therebetween. Thegap is automatically adjusted in response to load variations. When theload is low, the gap increases and the flow rate increases, and when theload is high, the elastic support portions 4 sag to decrease the gap,and required fluid pressure is ensured.

In addition, by connecting the frame plate 19 to the thin metal plate18, the thin portion and the thick portion are provided in the loweropposed wall 5B. In this configuration, the thin portion is preferablyset such that its resonant frequency is substantially the same as orslightly lower than that of the actuator 3. Thus, the thin portionflexurally vibrates in response to pressure variation caused byvibrations of the actuator 3, such that its vibration phase shifts fromthe vibration phase of the actuator 3 (for example, a delay of about90°), and thus, it is possible to substantially increase the vibrationamplitude in the interval between the actuator 3 and the lower opposedwall 5B in order to further improve the pumping power. The thin metalplate 18 and the frame plate 19 may preferably be made of resin, insteadof metal, for example. However, in the present preferred embodiment, thethin metal plate 18 and the frame plate 19 are made of metal in order toachieve a resonant frequency that is substantially the same as that ofthe actuator 3.

Next, a result of a sample test conducted using the piezoelectric pump 1having the configuration described above will be described withreference to FIG. 8. A sample A is a comparative sample in which thenatural vibration frequency of the spring portion is intentionallyshifted from the natural vibration frequency of the actuator.Specifically, in the sample A, the material of the leaf spring isphosphor bronze (C5210), the designed value of the natural vibrationfrequency of each elastic support portion is set to about 17.4 kHz, andthe natural vibration frequency of the actuator is set to about 20 kHz,for example. Meanwhile, in a sample B, the material of the leaf springis German silver (C7701), the designed value of the natural vibrationfrequency of each elastic support portion is set to about 19.8 kHz, andthe natural vibration frequency of the actuator is set to about 20 kHz,for example.

In such a sample test, it was confirmed that in the sample B in whichthe natural vibration frequency of each elastic support portion issubstantially equal to the natural vibration frequency of the actuator,the obtained fluid pressure and flow rate are greater than in the sampleA in which the natural vibration frequency of each elastic supportportion is different from the natural vibration frequency of theactuator, as shown in FIG. 8. This is because damping of flexuralvibrations by each elastic support portion is prevented or minimized.

Next, a configuration of another example of the leaf spring according toa preferred embodiment of the present invention will be described.

FIG. 9 is a plan view of a leaf spring 15A according to the otherexample. The leaf spring 15 includes three separately provided elasticsupport portions 4, whereas the leaf spring 15A is configured to includean annular beam portion 25A, six side wall connection portions 27Apreferably arranged at intervals of about 60°, for example, and sixactuator connection portions 26A arranged so as to be shifted from theside wall connection portions 27A preferably by about 30°, for example.

In the present preferred embodiment, when the resonant frequency(natural vibration frequency) of the elastic support portionsubstantially corresponds with the resonant frequency (natural vibrationfrequency) of the actuator and the elastic support portion vibrates inthe first-order resonance mode or in a higher odd number-order resonancemode, flexural vibrations of the actuator are prevented from beingdamped. It should be noted that the resonant frequency (naturalvibration frequency) of the elastic support portion is not limited toexactly corresponding to the resonant frequency (natural vibrationfrequency) of the actuator, and may be slightly shifted therefrom in arange in which the advantageous effects are provided.

Second Preferred Embodiment

Next, a piezoelectric pump 51 according to a second preferred embodimentof the present invention will be described.

FIG. 10 is an exploded perspective view of the piezoelectric pump 51.The piezoelectric pump 51 includes an actuator 53 and a thin metal plate58 each of which has a different configuration from that in the firstpreferred embodiment of the present invention described above.

The actuator 53 includes a piezoelectric element 3B, a reinforcing plate55, a leaf spring 56, and a reinforcing plate 55 that are laminated in amiddle portion thereof. In this case, it is necessary to appropriatelyreset the coefficient of linear expansion of each member, and it ispreferable that a material having a sufficiently higher coefficient oflinear expansion than those of the piezoelectric element 3B and the leafspring 56 is used for the reinforcing plate 55. Preferably, for example,phosphor bronze, German silver, or other suitable material having a highcoefficient of linear expansion is used for the reinforcing plate 55,and SUS430 or other suitable material having a low coefficient of linearexpansion is used for the leaf spring. In this case, the Young's modulusof the leaf spring is higher than those of phosphor bronze and Germansilver, and thus, the spring constant and the natural vibrationfrequency of the leaf spring are too high when the leaf spring has thesame spring shape as in the first preferred embodiment. Therefore, inthe present preferred embodiment, the natural vibration frequency isreduced preferably by changing the shape of the leaf spring, such as byincreasing the length of the slit portion so as to be greater than thelength of the slit portion in the first preferred embodiment.

In addition, in the present preferred embodiment, in the thin metalplate 58, relief holes 58A are provided in positions that face theelastic support portions of the leaf spring 56. The relief holes 58Aprevent interference between the leaf spring 56 and the thin metal plate58. With the configuration of preferred embodiments of the presentinvention, the elastic support portions vibrate in response tovibrations of the actuator, and in each elastic support portion, thevicinity of the connection portion to the actuator has the highestvibration amplitude. Although there is no problem in the first preferredembodiment, when the reinforcing plate and the piezoelectric element areprovided on the leaf spring as in the present preferred embodiment, theinterval between the leaf spring 56 and the thin metal plate 58 is onlyabout 20 μm, for example, and there is a possibility that the elasticsupport portion will come into contact with the thin metal plate 58during driving. Contact between the elastic support portion and the thinmetal plate 58 is problematic since it deteriorates the pressure-flowrate characteristic and causes unusual noise. Thus, by providing therelief holes 58A in the portions of the thin metal plate 58 that facethe elastic support portions, interference between the elastic supportportions and the thin metal plate 58 is prevented. It should be notedthat a lifting effect by flow path resistance is exerted in the vicinityof the center portion of the actuator, and thus, contact with the thinmetal plate 58 is unlikely to occur, which causes no problem.

The relief holes are preferably provided in six positions in the presentpreferred embodiments so as to support leaf springs having variousshapes. However, when three elastic support portions are provided as inthe present preferred embodiment, relief holes may merely be provided inthe three corresponding positions, respectively.

In each of the preferred embodiments described above, a unimorph typeactuator preferably is provided in which the piezoelectric element isdisposed on a single surface of the leaf spring. However, a bimorph typeactuator may be provided in which piezoelectric elements are disposed onboth surfaces of a leaf spring.

In addition, the actuator is not limited to the type including thepiezoelectric element, and one that is driven by an electromagneticdrive may be used as long as it flexurally vibrates.

In addition, the sizes of the piezoelectric element and the disc portionmay be the same, or the disc portion may be larger than thepiezoelectric element.

In addition, in preferred embodiments of the present invention, inapplications in which occurrence of audible sound is not problematic,the actuator may be driven in an audible frequency band.

In addition, the configuration is not limited to the configuration inwhich one flow path hole 6A is provided, and a plurality of flow pathholes 6A may be provided in a region that faces the actuator.

In addition, in each of the preferred embodiments described above, thefrequency of the drive voltage preferably is set such that the actuatorvibrates in the first-order mode. However, the frequency of the drivevoltage may be set such that the actuator vibrates in another mode, suchas the third-order mode.

In addition, in each of the preferred embodiments described above, thedisc-shaped piezoelectric element and the disc-shaped vibration plateare preferably provided. However, one of the piezoelectric element andthe vibration plate may be rectangular or polygonal.

It should be noted that the fluid to be sucked or sucked and dischargedis not limited to a gas and may be a liquid.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An actuator support structure comprising: aplate-shaped actuator arranged to flexurally vibrate from a centerportion of a principal surface thereof to an outer peripheral portionthereof; a side wall surrounding an outer periphery of the actuator; andat least one elastic support portion elastically supporting the outerperiphery of the actuator to the side wall; wherein the at least oneelastic support portion includes: a beam portion extending in a gapbetween the actuator and the side wall in a direction along the outerperiphery of the actuator; an actuator connection portion connecting thebeam portion to the actuator; and a side wall connection portionprovided in a position offset from the actuator connection portion inthe direction along the outer periphery of the actuator and connectingthe beam portion to the side wall.
 2. The actuator support structureaccording to claim 1, wherein the beam portion is connected to theactuator via the actuator connection portion at a position adjacent to aloop of natural vibrations when the side wall connection portion definesa fixing portion, and a natural vibration frequency of the naturalvibrations corresponds or substantially corresponds to a naturalvibration frequency of the actuator.
 3. The actuator support structureaccording to claim 2, wherein two of the side wall connection portionsare connected to both ends of the beam portion; and the actuatorconnection portion is connected to a center portion of the beam portionbetween the both ends thereof.
 4. The actuator support structureaccording to claim 2, wherein vibrations of the beam portionaccompanying the flexural vibrations of the actuator are vibrations in afirst-order resonance mode.
 5. The actuator support structure accordingto claim 1, wherein the actuator has a disc shape.
 6. The actuatorsupport structure according to claim 1, wherein the actuator includes apiezoelectric element arranged to vibrate the actuator.
 7. The actuatorsupport structure according to claim 1, wherein the at least one elasticsupport portion includes three elastic support portions.
 8. The actuatorsupport structure according to claim 7, wherein the three elasticsupport portions are spaced apart from one another in the directionalong the outer periphery of the actuator at intervals of about 120°. 9.The actuator support structure according to claim 1, wherein the atleast one elastic support portion includes an annular beam portion, sixside wall connection portions arranged in the direction along the outerperiphery of the actuator at intervals of about 60° and six actuatorconnection portions arranged in the direction along the outer peripheryof the actuator so as to be shifted from the side wall connectionportions by about 30°.
 10. A pump device comprising: a plate-shapedactuator arranged to flexurally vibrate from a center portion of aprincipal surface thereof to an outer peripheral portion thereof; ahousing including a side wall surrounding an outer periphery of theactuator and an opposed wall which is adjacent to and opposed to theprincipal surface of the actuator; and an elastic support portionelastically supporting the outer periphery of the actuator on the sidewall; wherein the elastic support portion includes: a beam portionextending in a gap between the actuator and the side wall in a directionalong the outer periphery of the actuator; an actuator connectionportion connecting the beam portion to the actuator; and a side wallconnection portion provided in a position offset from the actuatorconnection portion in the direction along the outer periphery of theactuator and connecting the beam portion to the side wall; and theopposed wall includes a flow path hole in a center portion of a regionfacing the actuator or in an area surrounding the center portion throughwhich a fluid flows.
 11. The pump device according to claim 10, whereinthe beam portion is connected to the actuator via the actuatorconnection portion at a position adjacent to a loop of naturalvibrations when the side wall connection portion defines a fixingportion, and a natural vibration frequency of the natural vibrationscorresponds or substantially corresponds to a natural vibrationfrequency of the actuator.
 12. The pump device according to claim 11,wherein two of the side wall connection portions are connected to bothends of the beam portion; and the actuator connection portion isconnected to a center portion of the beam portion between the both endsthereof.
 13. The pump device according to claim 11 wherein vibrations ofthe beam portion accompanying the flexural vibrations of the actuatorare vibrations in a first-order resonance mode.
 14. The pump deviceaccording to claim 10, wherein the actuator has a disc shape.
 15. Thepump device according to claim 10, wherein the opposed wall includes: athin portion which is provided on an outer periphery of the flow pathhole and capable of flexurally vibrating; and a thick portion which isprovided on an outer periphery of the thin portion.
 16. The pump deviceaccording to claim 10, wherein the actuator includes a piezoelectricelement arranged to vibrate the actuator.
 17. The pump device accordingto claim 10, wherein the at least one elastic support portion includesthree elastic support portions.
 18. The pump device according to claim17, wherein the three elastic support portions are spaced apart from oneanother in the direction along the outer periphery of the actuator atintervals of about 120°.
 19. The actuator support structure according toclaim 10, wherein the at least one elastic support portion includes anannular beam portion, six side wall connection portions arranged in thedirection along the outer periphery of the actuator at intervals ofabout 60° and six actuator connection portions arranged in the directionalong the outer periphery of the actuator so as to be shifted from theside wall connection portions by about 30°.
 20. The actuator supportstructure according to claim 10, wherein a portion of the actuator, aportion of the housing, and the elastic support portion are defined by aleaf spring.